This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Hepatitis C Virus results in persistent infections in over 70% of infected individuals. Chronic infections often lead to chronic liver disease, cirrhosis and hepatocellular carcinoma. Of the nearly 3 million Americans infected with HCV, there are about 10,000 deaths each year due to liver complications. There is presently no vaccine to prevent HCV infections. It is believed that T lymphocytes are responsible for clearing HCV infections in those who are able to control the virus before it becomes persistent. In previous chimpanzee experiments, we have shown that acutely infected chimpanzees that naturally clear the infection can be re-infected by an identical virus. This second infection is quickly controlled and the virus rapidly cleared. We have also shown that this control is mediated by rapid expansion of HCV-specific memory T-cells. We wish to qualitatively analyze the recall T-cell response in recovered rechallenged chimpanzees so that biomarkers can be established to determine if developed T-cell vaccines will be effective at preventing viral disease. The results of this study will greatly reduce the use of chimpanzees for future experimentation and enhance the efficacy of HCV vaccines.